The increasing share of renewable energy sources is reducing the number of synchronous generators in the grid and therewith reducing system inertia. This results in faster frequency deviations, which could compromise grid stability. Transmission system operators (TSOs) are therefore implementing various measures to maintain the grid inertia.

This paper presents an overview of technical solutions for fast frequency support from grid-connected hybrid power plants, including inertia from synchronous condensers and synthetic inertia delivered by battery energy storage systems (BESS). The situation in The Netherlands and Germany is discussed regarding the development of a commercial market for synthetic inertia from grid-forming converters.

A case study is presented of a grid-connected hybrid power plant consisting of a 20 MW BESS integrated into a 90 MW wind farm connected to the 150 kV grid, where a third resource specifically for inertia support may be added. Two options are considered: a synchronous condenser with flywheel and an additional BESS equipped with synthetic inertia functionality. RMS simulations of the inertial response with the synchronous condenser are used to derive converter rating requirements for the additional BESS to deliver a comparable response.